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Annals of Botany 85 : 159–166, 2000
doi : 10.1006\anbo.1999.1006, available online at http:\\www.idealibrary.com on
BOTANICAL BRIEFING
Resurrection Plants and the Secrets of Eternal Leaf
PETER SCOTT
School of Biological Sciences, UniŠersity of Sussex, Brighton, BN1 9QG, UK
Received : 21 April 1999
Returned for revision : 20 September 1999
Accepted : 24 September 1999
Most higher plants possess a phase in their life cycle in which tissues can survive desiccation. However, this is
restricted to specialized tissues such as seeds and pollen. Resurrection plants are remarkable in that they can tolerate
almost complete water loss in their vegetative tissues. The desiccated plant can remain alive in the dried state for
several years. However, upon watering the plants rehydrate and are fully functional within 48 h. Underpinning this
amazing ability is the capacity to accumulate large amounts of sucrose in the tissues. This sugar has the property of
stabilizing enzymes and cellular structures in the absence of water. The sources of carbon that fuel sucrose synthesis
are not known, but temporary carbohydrate stores and photosynthesis are the most likely candidates. On rewatering,
the sucrose is metabolized rapidly as the tissues rehydrate. Increased expression of a number of genes in response to
drought stress have been noted. A number of these are associated with metabolic pathways linked with primary
carbohydrate metabolism. However, some genes related to LEA (Late Embryogenic Abundant) proteins have been
isolated which suggests they too may play a role in maintaining tissue integrity during desiccation. How these
mechanisms are integrated to enable resurrection plants to survive desiccation is discussed.
# 2000 Annals of Botany Company
Key words : ABA, Craterostigma, desiccation tolerance, poikilohydric, resurrection.
INTRODUCTION
Some higher plant species are well adapted to arid
environments through mechanisms that mitigate drought
stress, including both physiological and biochemical adaptations. Physiological adaptations take many forms ranging
from partial senescence of tissues, to structural adaptations
such as water storage organs and restrictions in surface area
of aerial tissues as seen in Cactaceae and Euphorbiaceae.
Biochemical adaptations range from damage limitation
mechanisms to additions to photosynthetic pathways such
as crassulacean acid metabolism (Smith and Bryce, 1992).
All of these mechanisms are very effective and they allow
plants to inhabit a wide range of arid environments, but
when subjected to prolonged lack of water these plants will
dehydrate and die. Although these mechanisms allow plants
to lessen the severity of drought stress they do not make the
plant tolerant of desiccation.
However, there is a group of higher plants known as
poikilohydric or resurrection plants, which possess a
uniquely effective mechanism for coping with drought stress
by being desiccation tolerant. Virtually all plant species, at
some point in their life cycle, are at least partially tolerant
of desiccation. For example, seeds and pollen frequently
lose large quantities of water during their maturation
process (Bewley, 1979). But the ability of mature tissue,
such as roots and leaves, to survive virtually complete
desiccation is very rare. Resurrection plants survive the loss
of most of their tissue water content until a quiescent stage
E-mail Bafy2!sussex.ac.uk
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is achieved. Upon watering the plants rapidly revive and are
restored to their former state. This resurrection capacity is
not restricted to the main meristems of these plants. Fully
mature leaves can lose up to 95 % of their water content and
then, upon rewatering, the leaves are rehydrated and are
fully photosynthetically active within 24 h (Bernacchia
et al., 1996). Tissue damage through this drying and
rehydration process appears to be minimal to non-existent.
Unlike other plant responses to drought stress, desiccation
in resurrection plants prevents growth and reproduction
over the dehydrated period. Instead the plant is preserved
until water becomes available ; at this point it is ready to
take immediate advantage of the new conditions. Thus a
resurrection plant has a great competitive advantage over
other species for certain ecological niches. In severely
drought stressed areas, the plant can remain quiescent for
considerable periods of time, but at the first substantial fall
of rain it can resurrect, and grow and reproduce long before
other species have the opportunity to do so.
RESURRECTION PLANTS
Small numbers of resurrection plant species are represented
in most taxonomic groups, ranging from pteridophytes to
dicotyledons. This topic has been reviewed thoroughly very
recently by Hartung et al. (1998). Among these species there
are both terrestrial species such as the monocotyledonous
plant, Xerophyta Šiscosa (Baker) and the dicotyledonous
shrub Myrothamnus fabellifolia (Welw.), and an aquatic
species Chamaegigas intrepidus (Dinter). As would be
expected, most resurrection plant species are native to arid
# 2000 Annals of Botany Company
160
Scott—Physiology of Resurrection Plants
F. 1. A–F, Dehydration and rehydration phases of resurrection in Craterostigma plantagineum. On day 1 watering ceased (A). Photographs
were taken of the same plant for the following 19 d. C shows the fully dehydrated plant. In D the dehydrated plant was watered and then
photographs were taken of the plant regularly to follow the physiological processes up to 24 h after the initial watering. E shows a flowering
Craterostigma plant 2 weeks after the initial watering.
climates in the world such as southern Africa, southern
America, and western Australia (Gaff, 1977, 1987). Resurrection plants inhabit ecological niches that are subjected
to lengthy periods of drought with periods of rain during
the year. They are frequently found as denizens of rocky
outcrops, possessing the ability to grow in shallow, sandy
soils (Sherwin and Farrant, 1995). Their habitats often take
the form of delves on rock outcrops which have the capacity
to form ephemeral pools (Gaff, 1971 ; Gaff and Giess, 1986).
The surrounding rock surface acts to broaden the water
catchment area for the plants, so only a couple of millimetres
of rain can result in a large accumulation of water in pools.
However, the pools formed are temporary, lasting only for
a few days at best. The growth and reproduction of the
plant occurs in these wet seasons, but upon drying the
plants can remain dormant for considerable time periods.
The aquatic plant Ch. intrepidus has been known to survive
for up to 11 months in the dehydrated state (Hartung et al.,
Scott—Physiology of Resurrection Plants
1998). However, this period is short compared to
Craterostigma species which have been known to last at
least 2 years without water, and probably much longer.
Mechanisms that protect plants from water stress are
frequently effective against other environmental stresses,
and resurrection plants are no exception, for example, up to
three out of five species of resurrection grasses tested have
been shown to be salt tolerant (Gaff and Wood, 1988 ; Gaff,
1989). In addition, it has been postulated that resurrection
plants should be resistant to large fluctuations in temperature (Hartung et al., 1998). This is certainly a necessity
for species such as Craterostigma plantagineum (Hochst.)
which inhabits granite outcrops in southern Africa, where
rock surfaces can reach over 60 mC in the dry season (Dinter,
1918). Thus the ability to survive desiccation enables
resurrection plants to inhabit ecological niches uninhabitable by most higher plant species.
RESURRECTION PHYSIOLOGY
Given that resurrection plants are found in many plant
families, the ability to tolerate desiccation must have arisen
numerous times during evolution, and a common physiological basis of how this ability is achieved in plants is
therefore unlikely. A similar situation is apparent in CAM
plants. CAM species are represented in a wide range of
plant families, and although the general malate shuttle
5
100
75
3
50
2
25
1
A
0
0
100
3
75
Percentage water content
Chlorophyll content (mg Chl g–1 d.wt)
4
2
50
1
25
B
0
6
8 10 12 14 16 18
Time of dehydration (d)
0
F. 2. Measurements of percentage water content and chlorophyll
content in young and mature leaves of Craterostigma plantagineum
during dehydration. The chlorophyll content () and percentage water
content ($) (f.wtkd.wt)\(f.wti100) were calculated for Craterostigma
plants as they were dehydrated. The leaf types are : young (less than
70 % of the final mature size) (A) and mature (B). The results are means
ps.e. from four replicate measurements from different plants.
161
scheme is common to all species, there are numerous
metabolic differences between them (Leegood, von Caemmerer and Osmond, 1997). Thus studying a single resurrection plant is unlikely to explain what occurs in all
species, but it is becoming clear that some generalizations
can be made. Despite the remarkable abilities of resurrection
plants only a minority of species have been studied in any
detail, with most physiological and biochemical work being
performed on the genus Craterostigma, a member of the
Scrophulariaceae family. Hence Craterostigma has become
the model subject for research.
To illustrate the resurrection process, a series of photographs and measurements of the relative water content and
chlorophyll amounts in the young and mature leaves of C.
plantagineum are shown in Figs 1 and 2. One of the most
remarkable features of C. plantagineum is its ability to
shrink during dehydration. This can be seen in the
photographs (Fig. 1A–D) and this shrinkage correlates with
the point in time when the leaves lose most of their water
content (Fig. 2). It has been estimated that leaves of C.
plantagineum drop to around 15 % of their original area
(Hartung et al., 1998). How the leaves achieve this reduction
in size is not yet clear, but there is some evidence that the
plasmalemma and the cell wall form a concertina that
minimizes damage within and between cells. Similar
shrinkage has also been observed in Ch. intrepidus, where
leaves shrink to 25 % of their original size (Schiller et al.,
1999). In woody species such as M. fabellifolia such severe
shrinkage is not seen, but the final relative water content of
aerial tissues of this species in the desiccated state is
remarkably similar to that reported for Craterostigma
(RWC approx. 5–10 %).
In contrast to what is known to be occurring in the leaves,
very little research has been performed on the roots of
resurrection plants. In such tissues the response to drought
stress is probably more rapid than in the leaves since it is the
roots which will first sense a soil water deficit. In addition,
the roots are very much more restricted in their ability to
shrink during dehydration since they are embedded in a
solid soil matrix. Thus shrinkage of roots beyond that of the
soil could result in major root network damage.
Another aspect of the physiology of resurrection plants
that has only just begun to receive attention is the response
of the xylem to desiccation (Sherwin et al., 1998). The
problem is how can the tissue dry out and then reactivate on
resurrection ? This is no small problem since the formation
of air bubbles in the xylem tissue is a well-known cause of
xylem blockage (Sperry and Tyree, 1988). The solution in
M. fabellifolia has been suggested to be narrow reticulate
xylem vessels, which cavitate on desiccation of the plant, but
refill from capillarity and root pressure on resurrection
(Sherwin et al., 1998).
Angiosperms that are resurrection plants have been
subdivided into two further groups : homoiochlorophyllous
plants, which retain their chlorophyll during drying (such as
Craterostigma wilmsii (Engl.) and M. fabellifolia), and
poikilochlorophyllous plants, which lose chlorophyll on
drying (such as X. Šiscosa) (Tuba et al., 1993, 1994 ; Sherwin
and Farrant, 1995). The loss of chlorophyll in C. plantagineum is clearly seen in Fig. 2. The fall in chlorophyll
162
Scott—Physiology of Resurrection Plants
content in the leaves of X. Šiscosa is accompanied by the
accumulation of anthocyanins (Sherwin and Farrant, 1998).
The processes of dismantling the photosynthetic apparatus
and the synthesis of anthocyanins are thought to be linked
to the protection of plants against UV-light and from
damage as a result of oxygen free radical generation during
desiccation (Smirnoff, 1993 ; Smirnoff and Colombe! , 1993 ;
Sherwin and Farrant, 1998).
One final remarkable feature of resurrection plants is
their ability to rehydrate very rapidly. The slowest
documented recovery is for M. fabellifolia, which takes
approx. 48 h to recover from the desiccated state when
watered from the soil alone. Plants such as C. plantagineum
can routinely revive within less than 24 h. This enables these
plants to rapidly take advantage of changes in water
availability.
METABOLIC CHANGES DURING
R E S U R R E C T I O N C Y C L ES
Numerous metabolic changes have been found to occur in
resurrection plants as they dehydrate and rehydrate.
However, the most thoroughly investigated is that of
carbohydrate accumulation. Table 1 shows a summary of
measurements of major carbohydrates present in fully
hydrated and dehydrated leaves from a range of resurrection
plants. In all resurrection plants sucrose is the dominant
carbohydrate to accumulate. A minimum of 72 µmol g−"
d.wt of sucrose appears to be sufficient to protect the
desiccated plant, but data are, as yet, unavailable to judge
whether plants with higher final sucrose contents are more
desiccation tolerant than other species. C. plantagineum
stands out from the other species, accumulating almost
three-times more sucrose than the highest of the other plant
species ; why there should be such an excess is not
understood. Another feature that stands out from the data
in Table 1 is that, for some unknown reason, measurements
of sucrose and trehalose in identical plant species by
different laboratories are very variable. Although it has
been suggested that trehalose accumulation is also significant, the data in Table 1 provide no compelling evidence
that trehalose accumulates in resurrection plants during
dehydration. Only in a single case, M. fabellifolia (Drennan
et al., 1993), has trehalose been reported to accumulate to
any great extent, and this finding is controversial (Bianchi et
al., 1993).
Accumulation of sucrose in tissues of resurrection plants
has been proposed to protect the dehydrated cell (Ingram
and Bartels, 1996). There are two hypotheses concerning the
role of the accumulated sugars. First, the sugars could act to
stabilize membranes and proteins in the dry state by
maintaining hydrogen bonding within and between macromolecules (Crowe et al., 1986 ; Allison et al., 1999). Secondly,
the sugars could vitrify the cell contents and stabilize
internal cell structure (Crowe et al., 1996). Recent evidence
strongly supports a combination of these two processes
enabling the maintenance of cell integrity during dehydration (Crowe et al., 1998).
The accumulation of sucrose in tissues of resurrection
plants may account for a large part of the acquired
desiccation tolerance, but is it all that is required ? The
definitive experiments have yet to be performed, but
indications from early experiments look promising. In
experiments where isolated enzymes have been dried in the
presence of sucrose there is good evidence that the enzymes
remain stable in the dried state (Bustos and Romo, 1996 ;
Suzuki et al., 1997). Parallel work on isolated membrane
vesicles also supports the view that sucrose preserves the
integrity of the lipid bilayer during dehydration (Crowe et
al., 1998). Other research has investigated whether a simple
living system can be desiccated. E. coli cells, which are
desiccation intolerant, have been preserved in sucrose or
trehalose (Leslie et al., 1995). Although the cells exhibited
poor survival rates during desiccation and over time, this
may be since the E. coli cells do not take up the sugar
sufficiently to ensure maximum protection. Data such as
T     1. Carbohydrate content in fully hydrated and desiccated leaŠes of a range of different resurrection plant species
Sucrose content
Plant species
Hydrated
Trehalose content
Dehydrated
Hydrated
Dehydrated
Reference
(µmol g−" d.wt)
C. plantagineum
M. fabellifolia
R. nathaliae
R. myconi
H. rhodopensis
X. Šillosa
Tripogon jacquemontii
S. stapfianus
Desiccation intolerant species
S. pyramidalis
73
88
383
58
96
60
43
15
236
9
2000
169
463
294
204
170
81
72
772
95
ND
81
148
ND
ND
ND
ND
0n2
ND
0n0
ND
105
136
ND
ND
ND
ND
1n0
ND
2n0
Bianchi et al., 1991
Drennan et al., 1993
Bianchi et al., 1993
Mu$ ller et al., 1997
Mu$ ller et al., 1997
Mu$ ller et al., 1997
Ghasempour et al., 1998
Ghasempour et al., 1998
Albini et al., 1994
Ghasempour et al., 1998
45
36
NM
NM
Ghasempour et al., 1998
The amounts of sucrose and trehalose in fully hydrated and dehydrated leaves of eight different species of resurrection plants and one species
that is desiccation intolerant. ND, Not detectable ; NM, not measured.
Scott—Physiology of Resurrection Plants
these have fuelled a great deal of interest in the use of sugars
as a mechanism for protection of other living tissues (PilonSmits et al., 1998 ; Zentella et al., 1999).
Given the general nature of sucrose accumulation during
tissue dehydration it appears to be a vital requirement in the
desiccated state. Therefore, to understand the dehydration
phase of the resurrection cycle the source for this accumulation must be identified. This area has received very
little attention to date and the main evidence is circumstantial and correlative, but conclusive proof of the
carbon sources is lacking. As sucrose accumulates in C.
plantagineum similar quantities of an eight carbon carbohydrate, 2-octulose, are metabolized (Bianchi et al., 1991 ;
Ingram and Bartels, 1996). This has led to the proposal that
carbon in 2-octulose is used as a source for sucrose
accumulation. This conversion could account for up to
80 % of the carbohydrate accumulated in leaves of
Craterostigma. The remainder would have to be derived
from alternative sources. Other resurrection plants lack the
presence of 2-octulose as a possible reserve for sugar
accumulation, and thus other carbohydrate sources are
essential for survival. As sucrose accumulates in Ramonda,
the starch content of the leaf declines. However, starch
metabolism can only account for less than 20 % of the
accumulated sugar. This leaves photosynthesis and the
possibility of carbohydrate reserves outside of the leaf as the
other major carbon sources (Mu$ ller et al., 1997). In X.
Šiscosa, as leaves dry, glucose and fructose accumulate
initially. There are insufficient measurements to enable
comment on the source of carbon used for their accumulation but photosynthesis is the most likely candidate.
As the plant desiccates, the hexoses are metabolized and
sucrose accumulates as the dominant carbohydrate in the
dehydrated plant. The advantage that Craterostigma
appears to possess over the other resurrection plants is a
large carbohydrate store of 2-octulose in hydrated leaves.
Hence Craterostigma is not completely reliant upon photosynthesis for desiccation tolerance and is theoretically able
to respond rapidly to sudden falls in water availability
through the use of 2-octulose reserves.
The carbon source that fuels the accumulation of sugars
during desiccation underpins the ability of poikilohydric
plants to resurrect. Given their habitats it is clear that the
environmental conditions in which the plants live can
change in a short space of time (Gaff and Giess, 1986).
Hence, in order to be desiccation tolerant, a plant must
possess the capacity to protect itself as rapidly as possible.
The synthesis of carbohydrate through photosynthesis may,
under certain circumstances, be too slow to produce sufficient
sugar, hence the need for other storage carbohydrates. In
order to assess this we need the following data : (1) the rate
of photosynthesis ; (2) the amount of sugar accumulated by
a species ; (3) the time period over which the species is dried.
This is not yet available for any species. In every instance
where measurements of photosynthetic rate are provided
(Schwab et al., 1989 ; Deltoro et al., 1998 ; Hartung et al.,
1998), either sugar accumulation data or the drying period
are lacking.
With the huge changes in metabolic fluxes described
earlier it is hardly surprising that there have been several
163
reports documenting alterations in mRNA encoding enzymes vital for catalysis of these fluxes (Velasco, Salamini
and Bartels, 1994 ; Bernacchia et al., 1995 ; Ingram et al.,
1997 ; Kleines et al., 1999). However, such measurements
really do not tell us a great deal about the biochemistry of
desiccation tolerant plants. Measurements of a whole battery
of actual enzyme activities need to be performed if we are
ever to understand the metabolic basis for sugar accumulation.
CHANGES IN PROTEIN EXPRESSION IN
RESPONSE TO DROUGHT STRESS
Other than genes associated with metabolic pathways, there
are several other genes identified as being elevated in
expression during desiccation of resurrection plants. This
area has been reviewed recently by Ingram and Bartels
(1996), so only advances since their review will be discussed
here. In Craterostigma, several genes have been isolated
which possess homology with LEA (Late Embryogenesis
Abundant) proteins ; other genes have unknown functions
(Piatkowski et al., 1990 ; Ingram and Bartels, 1996). LEAs
are associated with the later stages of embryo development
in seeds. Since many seeds are desiccation tolerant to some
degree, then the presence of LEAs in resurrection plants is
not surprising. The difficulty with these proteins is the lack
of an understanding of their actual role in desiccation
(Baker et al., 1988). From their sequences it is likely they
have no functional role as enzymes, but they have been
proposed to associate with internal structures of cells to
stabilize them during dehydration. Thus they may act to
supplement the protection afforded by sucrose accumulation. Two further genes have been isolated which encode
putative homeodomain-leucine zipper proteins, CPHB-1
and -2 (Frank et al., 1998). Their action is implicated in the
regulation of expression of different sets of genes involved in
the dehydration process in Craterostigma plantagineum.
Similar sets of genes have been identified in the resurrection grass S. stapfianus. In this species six cDNA clones
have been isolated that have increased expression in leaves
during drought stress (Blomstedt et al., 1998). Some of these
genes bear homology to genes from other plant species
thought to be involved in the maintenance of cell integrity
during water stress e.g. dehydrins, LEAs and thiol proteases.
One of the major difficulties in understanding the role of
changes in protein expression during the resurrection cycle
of poikilohydric plants is that during the dehydration phase
genes also need to be expressed for the rehydration phase.
Hence it is difficult to conclude at which point the protein
carries out its function. Through the use of inhibitors of
protein synthesis in Xerophyta humilis (Bak.) it has been
observed that most of the components and organization for
the start of the resurrection phase are already present in the
plants during the dehydration phase (Dace et al. 1998).
SIGNAL PATHWAYS
One common feature of proteins that have been isolated
and identified as being increased in terms of expression
during tissue dehydration in resurrection plants has been
164
Scott—Physiology of Resurrection Plants
F. 3. Schematic representation of the dehydration and rehydration phase of the resurrection cycle in Craterostigma plantagineum. The scheme
combines research on the accumulation of ABA (Bartels et al., 1990), and sucrose (Schwall et al., 1995) in leaves during dehydration. ABA is likely
to be the first signal to leaves that water availability is diminished. The desiccation process is initiated. Upon rehydration the leaves rapidly expand
and in Craterostigma the plant flowers within 2 weeks of resurrection.
the inducibility with abscisic acid (Bartels et al., 1990). The
Craterostigma gene CdeT6-19 encodes a protein with a
sequence similar to LEA D11. The promoter for this gene is
induced by ABA or desiccation treatment (Michel et al.,
1994). This has fuelled speculation that ABA forms the
initial signal for metabolic events necessary for desiccation
tolerance. There is evidence for this hypothesis. An increase
in ABA concentration in leaves of Craterostigma occurs
during drought stress (Bartels et al., 1990 ; Schiller et al.,
1997). In addition, callus tissue derived in culture from
leaves of C. plantagineum can be dehydrated and become
desiccation tolerant only if treated with ABA prior to
dehydration (Bartels et al., 1990 ; Chandler et al., 1997).
Thus in the absence of roots, callus tissue can be induced to
maintain viability during desiccation by addition of ABA.
Furthermore, the addition of ABA to leaves of Craterostigma has been reported to induce sucrose accumulation,
but to date there are no published data to support this
statement (Schwall et al., 1995). Thus it is likely that ABA
is one of the crucial early signals required for the survival of
Craterostigma. A further gene has been isolated that is
implicated in the signal transduction pathway involving
ABA. The gene CDT-1 can be expressed constitutively in C.
plantagineum callus resulting in cells that no longer require
ABA treatment in order to survive desiccation (Furini et al.,
1997). CDT-1 is a novel gene sequence that may be involved
in activation of the signal pathway via regulatory RNA or
via a small polypeptide.
Large rises in leaf ABA content have been noted also in
Myrothamnus fabellifolia, Xerophyta humilis and a large
range of other resurrection plants (Gaff and Loveys, 1984 ;
Schiller et al., 1997). Hence ABA may be a general signal
that initiates metabolic changes for desiccation tolerance in
resurrection plants. This would be very similar to the
situation that occurs in other higher plants exposed to
drought stress (Jensen et al., 1996 ; Hare et al., 1999).
SUMMARY
A summary of the ability of Craterostigma to survive
dehydration and revive is presented in Fig. 3. The roots,
being in the soil, are most likely to detect a drop in water
Scott—Physiology of Resurrection Plants
availability first. ABA synthesis, and release by roots is a
common response in plants to drought stress. Once released,
ABA could activate batteries of genes required for metabolic
processes such as the accumulation of sucrose from either
stored carbohydrates or through an alteration in photosynthetic carbon partitioning. In addition, the synthesis of
other proteins is induced such as dehydrins and LEAs which
could help to stabilize the plant cells as they lose water.
Thus as the tissues dehydrate, leaves shrink, chlorophyll is
degraded, sucrose accumulates and ultimately the xylem
cavitates and the plants become desiccated. On addition of
water, the xylem refills and cells begin to take up water and
expand ; enzymes present in the tissues are activated, sucrose
is metabolized, and chlorophyll is resynthesized. Within
24 h the plant is restored and is reproductively active within
2 weeks.
FUTURE PERSPECTIVES
Our understanding of the resurrection process is still patchy.
More research is required on a greater range of species to
appreciate common elements that exist. Our understanding
of the carbohydrate sources used for sucrose synthesis is
incomplete and more work needs to be performed to
identify these. This will allow a better understanding of the
time frame required by these plants in order to become
desiccation tolerant. Research into the dehydration characteristics of roots has been neglected to date. This needs to be
addressed to investigate whether leaves and roots use
similar mechanisms. In addition, we still do not know how
a plant senses where it is in the resurrection cycle. For
example, how does the plant regulate sucrose synthesis
during rehydration ? The use of transgenic plants to study
metabolism in resurrection plants has yet to make any great
headway. Reported use of transgenic C. plantagineum plants
has been announced (Furini et al., 1994, 1997), but little
work has been done using this technique. In my own
laboratory transgenic methods with this plant have proven
generally unreliable. Thus there is still a need to develop this
area more fully and exploit the potential offered by
transgenic technologies. Transgenic studies of plant metabolism have proved enormously successful in C species and
$
there is a need to capitalize on the potential of this
technology in resurrection plants (Stitt and Sonnewald,
1995 ; Hebers and Sonnewald, 1996).
I will leave readers with one perplexing observation on
higher plants in general. Although a majority of plants have
a stage in their life cycle that can tolerate dehydration, it is
remarkable how few species can use these same mechanisms
to protect vegetative tissues such as leaves and roots during
severe drought stress conditions as resurrection plants do.
L I T E R A T U R E C I T ED
Albini F, Murelli C, Patritti G, Rovati M, Zienna P, Finizi P. 1994.
Low-molecular weight substances from the resurrection plant
Sporobolus stafianus. Phytochemistry 37 : 137–142.
Allison SD, Chang B, Randolph TW, Carpenter JF. 1999. Hydrogen
bonding between sugar and protein is responsible for inhibition of
dehydration-induced protein unfolding. ArchiŠes of Biochemistry
and Biophysics 365 : 289–298.
165
Baker J, Steele C, Dure L. 1988. Sequence and characterisation of 6
LEA proteins and their genes from cotton. Plant Molecular
Biology 11 : 277–291.
Bartels D, Schneider K, Terstappen G, Piatkowski D, Salamini F. 1990.
Molecular cloning of abscisic acid modulated genes which are
induced during desiccation of the resurrection plant Craterostigma
plantagineum. Planta 181 : 27–34.
Bernacchia G, Salamini F, Bartels D. 1996. Molecular characterization
of the rehydration process in the resurrection plant Craterostigma
plantagineum. Plant Physiology 111 : 1043–1050.
Bernacchia G, Schwall G, Lottspeich F, Salamini F, Bartels D. 1995. The
transketolase gene family of the resurrection plant Craterostigma
plantagineum : differential expression during the rehydration phase.
EMBO Journal 14 : 610–618.
Bewley JD. 1979. Physiological aspects of desiccation tolerance. Annual
ReŠiew of Plant Physiology 30 : 195–238.
Bianchi G, Gamba A, Murelli C, Salamini F, Bartels D. 1991. Novel
carbohydrate metabolism in the resurrection plant Craterostigma
plantagineum. Plant Journal 1 : 355–359.
Bianchi G, Gamba A, Limiroli CR, Pozzi N, Elster R, Salamini F,
Bartels D. 1993. The unusual sugar composition in leaves of the
resurrection plant Myrothamnus fabellifolia. Physiologia Plantarum
87 : 223–226.
Blomstedt CK, Gianello RD, Hamill JD, Neale AD, Gaff DF. 1998.
Drought-stimulated genes correlated with desiccation tolerance of
the resurrection grass Sporobolus stapfianus. Plant Growth and
Regulation 24LS10: 153–161.
Bustos RO, Romo CR. 1996. Stabilisation of trypsin-like enzymes from
Antarctic krill : Effect of polyols, polysaccharides and proteins.
Journal of Chemical and Technological Biotechnology 65 : 193–199.
Chandler JW, Abrams SR, Bartels D. 1997. The effect of ABA
analogues on callus viability and gene expression in Craterostigma
plantagineum. Physiologia Plantarum 99 : 465–469.
Crowe JH, Carpenter JF, Crowe LM. 1998. The role of vitrification in
anhydrobiosis. Annual ReŠiew of Physiology 60 : 73–103.
Crowe JH, Hoekstra FA, Nguyen KHN, Crowe LM. 1996. Is vitrification
involved in depression of the phase transition temperature in dry
phospholipids. Biochimica et Biophysica Acta 1280 : 187–196.
Crowe LM, Womersley C, Crowe JH, Reid D, Appel L, Rudolph A.
1986. Prevention of fusion and leakage in freeze-dried liposomes
by carbohydrates. Biochimica et Biophysica Acta 861 : 131–140.
Dace H, Sherwin HW, Illing N, Farrant JM. 1998. Use of metabolic
inhibitors to elucidate mechanisms of recovery from desiccation
stress in the resurrection plant Xerophyta humilis. Plant Growth
Regulation 24 : 171–177.
Deltoro VI, Calatayud A, Gimeno C, Abadia A, Barreno E. 1998.
Changes in chlorophyll a fluorescence, photosynthetic CO
#
assimilation and xanthophyll cycle interconversions during dehydration in desiccation tolerant and intolerant liverworts. Planta
207 : 224–228.
Dinter K. 1918. Botanische Reisen in Deutsch-Su$ dwest-Afrika. Feddes
Republic Bein 3 : 1–169.
Drennan PM, Smith MT, Goldsworth D, Van Staden J. 1993. The
occurrence of trehalose in the leaves of the desiccation tolerant
angiosperm Myrothamnus flabellifolia Welw. Journal of Plant
Physiology 142 : 493–496.
Frank W, Philips J, Salamini F, Bartels D. 1998. Two dehydrationinduced transcripts from the resurrection plant Craterostigma
plantagineum encode interacting homeodomain-leucine zipper
proteins. Plant Journal 15 : 413–421.
Furini A, Koncz C, Salamini F, Bartels D. 1994. Agrobacteriummediated transformation of the desiccation tolerant plant Craterostigma plantagineum. Plant Cell Reports 14 : 102–106.
Furini A, Koncz C, Salamini F, Bartels D. 1997. High level transcription
of a member of a repeated gene family confers dehydration
tolerance to callus tissue of Craterostigma plantagineum. EMBO
Journal 16 : 3599–3608.
Gaff DF. 1971. Desiccation tolerant plants in Southern Africa. Science
174 : 1033–1034.
Gaff DF. 1977. Desiccation tolerant vascular plants in southern Africa.
Oecologia 31 : 95–104.
Gaff DF. 1987. Desiccation tolerant plants in South America. Oecologia
74 : 133–136.
166
Scott—Physiology of Resurrection Plants
Gaff DF. 1989. Responses of desiccation tolerant resurrection plants to
water stress. In : Kreeb KH, Richter H, Hinckley TM, eds.
Structural and functional responses to enŠironmental stresses : water
shortage. The Hague : SBP Publishing, 255–268.
Gaff DF, Giess W. 1986. Drought resistance in water plants in rock
pools of southern Africa. Dinternia 18 : 17–36.
Gaff DF, Loveys BR. 1984. Abscisic acid content and effects during
dehydration of detached leaves of desiccation tolerant plants.
Journal of Experimental Botany 35 : 1350–1358.
Gaff DF, Wood JN. 1988. Salt resistant desiccation tolerant grasses.
Proceedings of the International Congress on Plant Physiology.
New Dehli, 984–988.
Ghasempour HR, Gaff DF, Williams RPW, Gianello RD. 1998. Contents
of sugars in leaves of drying desiccation tolerant flowering plants
particularly grasses. Plant Growth Regulation 24 : 185–191.
Hare PD, Cress WA, van Staden J. 1999. Proline synthesis and
degradation : a model for elucidating stress-related signal transduction. Journal of Experimental Botany 50 : 413–434.
Hartung W, Schiller P, Karl-Josef D. 1998. Physiology of poikilohydric
plants. Cell Biology and Physiology. Progress in Botany 59 :
299–327.
Hebers K, Sonnewald U. 1996. Manipulating metabolic partitioning in
transgenic plants. Trends in Biotechnology 14 : 198–205.
Ingram J, Bartels D. 1996. The molecular basis of dehydration
tolerance in plants. Annual ReŠiew of Plant Physiology and
Molecular Biology 47 : 377–403.
Ingram J, Chandler JW, Gallagher L, Salamini F, Bartels D. 1997.
Analysis of cDNA encoding sucrose phosphate synthase in relation
to sugar interconversions associated with dehydration in the
resurrection plant Craterostigma plantagineum Hochst. Plant
Physiology 115 : 113–121.
Jensen AB, Busk PK, Gigueras M, Alba M, Peracchia G. 1996. Drought
signal transduction in plants. Plant Growth Regulation 20 : 105–110.
Kleines M, Elster RC, Rodrigo MJ, Blervacq AS, Salamini F, Bartels D.
1999. Isolation and expression analysis of two stress-responsive
sucrose-synthase genes from the resurrection plant Craterostigma
plantagineum (Hochst.) Planta 209 : 13–24.
Leegood RC, von Caemmerer S, Osmond CB. 1997. Metabolite transport
and photosynthetic regulation in C and CAM plants. In : Dennis
%
DT, Turpin DT, Lefebvre DD, Layzell DB, eds. Plant metabolism.
Harlow, UK : Longman Press, 341–370.
Leslie SB, Israeli E, Lighthart B, Crowe JH, Crowe LM. 1995.
Trehalose and sucrose protect both membranes and proteins in
intact bacteria during drying. Applied and EnŠironmental Microbiology 61 : 3592–3597.
Michel D, Furini A, Salamini F, Bartels D. 1994. Structure and
regulation of an ABA- and desiccation-responsive gene from the
resurrection plant Craterostigma plantagineum. Plant Molecular
Biology 24 : 549–560.
Mu$ ller J, Sprenger N, Bortlik K, Boller T, Wiemken A. 1997. Desiccation
increases sucrose levels in Ramonda and Haberlea, two genera of
resurrection plants in the Gesneriaceae. Physiologia Plantarum
100 : 153–158.
Piatkowski D, Schneider K, Salamini F, Bartels D. 1990. Characterisation of five abscisic acid responsive cDNA clones isolated
from the desiccation-tolerant plant Craterostigma plantagineum
and their relationship to other water stress genes. Plant Physiology
94 : 1682–1688.
Pilon-Smits EA, Terry N, Sears T, Kim H, Zayed A, Hwang S, van Dun
K, Voogd E, Verwoerd TC, Krutwagen RWHH, Godijn OJM.
1998. Trehalose-producing transgenic tobacco plants show im-
proved performance under drought conditions. Journal of Plant
Physiology 152 : 525–532.
Schiller P, Wolf R, Hartung W. 1997. Abscisic acid (ABA) relations in
the aquatic resurrection plant Chamaegigas intrepidus under
naturally fluctuating environmental conditions. New Phytologist
136 : 603–611.
Schiller P, Wolf R, Hartung W. 1999. A scanning electron microscopical
study of hydrated and dehydrated submerged leaves of the aquatic
resurrection plant Ch. intrepidus. Flora 194 : 97–102.
Schwab KB, Schreiber U, Heber U. 1989. Response of photosynthesis
and respiration of resurrection plants to desiccation and rehydration. Planta 177 : 217–227.
Schwall G, Elster R, Ingram J, Bernacchia G, Bianchi G, Gallagher L,
Salamini F, Bartels D. 1995. Carbohydrate metabolism in the
desiccation tolerant plant Craterostigma plantagineum Hochst. In :
Pontis H, Salerno G, Echeverria E, eds. Sucrose metabolism,
biochemistry, physiology and molecular biology. Current topics in
Plant Physiology : 14. American Society of Plant Physiologists,
245–253.
Sherwin H, Farrant J. 1995. Surviving desiccation. Veld and Flora,
December, 119–121.
Sherwin H, Farrant J. 1998. Protection mechanisms against excess light
in the resurrection plants Craterostigma wilmsii and Xerophyta
Šiscosa. Plant Growth Regulation 24 : 203–210.
Sherwin H, Pammenter NW, February ED, Vander Willingen C, Farrant
J. 1998. Xylem hydraulic characteristics, water relations and wood
anatomy of the resurrection plant Myrothamnus fabellifolia Welw.
Annals of Botany 81 : 567-575.
Smirnoff N. 1993. The role of active oxygen in the response of plants to
water-deficit and desiccation. New Phytologist 125 : 27–58.
Smirnoff N, Colombe! SV. 1988. Drought influences the activity of
enzymes of the chloroplast hydrogen peroxide scavenging system.
Journal of Experimental Botany 39 : 1097–1108.
Smith JAC, Bryce JH. 1992. Metabolite compartmentation and
transport in CAM plants. In : Tobin AK, ed. Plant organelles.
Cambridge : Cambridge University Press, 141–167.
Sperry JS, Tyree MT. 1988. Mechanism of water stress-induced xylem
embolism. Plant Physiology 88 : 581–587.
Stitt M, Sonnewald U. 1995. Regulation of metabolism in transgenic
plants. Annual ReŠiew of Plant Physiology and Plant Molecular
Biology 47 : 377–403.
Suzuki T, Imamura K, Yamamoto K, Satoh T, Okazaki M. 1997.
Thermal stabilisation of freeze-dried enzymes by sugars. Journal of
Chemical Engineering of Japan 30 : 609–613.
Tuba Z, Lichtenhaler HK, Maroti I, Csintalan Z. 1993. Resynthesis of
thylakoids and functional chloroplasts in the desiccated leaves of
the poikilochlorophyllatous plant Xerophyta scabrida upon dehydration. Journal of Plant Physiology 142 : 742–748.
Tuba Z, Lichtenhaler HK, Csintalan Z, Nagy Z, Szente K. 1994.
Reconstitution of chlorophylls and photosynthetic CO assimi#
lation upon rehydration of the desiccated poikilochlorophyllatous
plant Xerophyta scabrida (Pax.). Planta 192 : 414–420.
Velasco R, Salamini F, Bartels D. 1994. Dehydration and ABA increase
mRNA levels and enzyme activity of cytosolic GAPDH in the
resurrection plant Craterostigma plantagineum. Plant Molecular
Biology 26 : 541–546.
Zentella R, Gallardo JO, van Dijck P, Mallol J, Bonini B, van Vaeck C,
Gaxiola R, Covarrubias AA, Sotelo J, Thevelein JM, Iturriaga G.
1999. A Selaginela lepidophylla trehalose-6-phosphate synthase
complements growth and stress-tolerance defects in a yeast tsp1
mutant. Plant Physiology 119 : 1473–1482.